1. Field of the Invention
The present invention relates to a cooling apparatus for cooling a heating body by boiling and condensing a refrigerant repeatedly.
2. Description of Related Art
A conventional cooling apparatus is disclosed in Japanese Patent Application Laid-Open No. 8-236669. In this cooling apparatus, as shown in FIG. 10, a boiling area in a refrigerant tank 1100 for reserving a refrigerant is increased to improve the radiation performance by attaching a heating body 1110 to the surface of the refrigerant tank 1100 and by arranging fins 1120 to correspond to the boiling face in the refrigerant tank 1100 for receiving the heat of the heating body.
Here, in the above-specified cooling apparatus, the fins 1120 arranged in the refrigerant tank 1100 form a plurality of passage portions 1130, in which the vaporized refrigerant (or bubbles), as boiled by the heat of the heating body 1110, rises. At this time, as referred to FIG. 5, some of the individual passage portions 1130 have more and less numbers of bubbles in dependence upon the position of the heating portion of the heating body 1110, and the number of bubbles increases the more for the higher position of the passage portions 1130 so that the small bubbles join together to form larger bubbles. In the passages of more bubbles, therefore, the boiling faces are covered with the more bubbles to lower the boiling heat transfer coefficient. As a result, the boiling face is likely to cause an abrupt temperature rise (or burnout).
Especially when the fin pitch is reduced to retain a larger boiling area, the passage portions 1130 are reduced in their average open area and are almost filled with the bubbles to reduce the quantity of refrigerant seriously so that the burnout may highly probably occur on the boiling faces.
Furthermore, in the cooling apparatus shown in FIG. 10, the fins 1120 arranged in the boiling portion form a plurality of passage portions 1130, through which vapor (or bubbles), as boiled by the radiation of a heating body, rises in the boiling portion. At this time, the quantity of generated vapor becomes the more as the vapor rises to the higher level. When the boiling portion is vertically long so that the fins 1120 arranged in the boiling portion are long or when the heat generated by the heating body increases although the fins 1120 are not vertically long, therefore, the vapor (or bubbles) is hard to come out from the passage portions 1130 formed by the fins 1120. As a result, the burnout becomes liable to occur on the upper side of the boiling portion so that the using range (or radiation) of the refrigerant tank 1100 is restricted.
Another conventional cooling apparatus is disclosed in Japanese Patent Application Laid-Open No. 8-204075. This cooling apparatus uses the principle of thermo-siphon and is constructed to include an evaporation portion 2100 for reserving a refrigerant and a condensation portion 2110 disposed over the evaporation portion 2100, as shown in FIG. 43. The vaporized refrigerant, as boiled in the evaporation portion 2100 by receiving heat of a heating body, flows into the condensation portion 2110. After that, the refrigerant is cooled and liquefied by the heat exchange with the external fluid, and is recycled to the evaporation portion 2100. By thus repeating the evaporation and condensation of the refrigerant, the heat of the heating body is transferred in the evaporation portion 2100 to the refrigerant and further to the condensation portion 2110 so that it is released to the external fluid at the condensation portion 2110.
In the cooling apparatus in FIG. 43, however, the condensed liquid, as liquefied in the condensation portion 2110, is returned to the evaporation portion 2100 via passages 2101 or returning passages 2102 of the evaporation portion 2100. In the passages 2101 within the mounting range of the heating body, however, the vaporized refrigerant, as boiled by the heat of the heating body, rises so that the condensed liquid and the vaporized refrigerant interfere as the counter flows. As a result, the vaporized refrigerant becomes hard to leave the evaporation portion 2100, and the condensed liquid flowing from the condensation portion 2110 into the evaporation portion 2100 is blown up by the vaporized refrigerant rising from the evaporation portion 2100 so that it becomes hard to return to the evaporation portion 2100. As a result, a burnout (or an abrupt temperature rise) is liable to occur on the boiling faces of the evaporation portion 2100, thus the radiation performance drops. By this problem, the drop in the radiation performance due to the burnout becomes the more liable to occur as the evaporation portion 2100 is thinned the more to reduce the quantity of precious refrigerant to be contained, from the demand for reducing the cost.
Still another conventional cooling apparatus is disclosed in Japanese Patent Application Laid-Open No. 9-126617. This cooling apparatus is used as a radiating device for an electric vehicle, and arranged inside a hood. Therefore, as shown in FIG. 56, in consideration of a mountability of inside hook in which arrangement space in a vertical direction is limited, a radiator 3100 is perpendicularly assembled to a refrigerant tank 3110 via a lower tank 3120, and the refrigerant tank 3110 is arranged at a large inclination.
In the still another cooling apparatus in FIG. 56, since the refrigerant tank 3110 is largely inclined, a liquid refrigerant in the refrigerant tank 3110 may flows back to the radiator side when, for example, the vehicle stops suddenly or ascends a uphill road. Therefore, it is difficult for a boiling face of the refrigerant tank 3110 to be stably filled with liquid refrigerant. In such a situation, the boiling face is likely to occur a burnout (abrupt temperature rising), a radiation performance may largely decrease. Especially when the condensed liquid amount becomes the less as the refrigerant tank 3110 is thinned the more, the burnout of the boiling faces are likely occur.
Furthermore, in the still another cooling apparatus in FIG. 56, a plurality of heating bodies 3130 are attached in the longitudinal direction of the refrigerant tank 3110. As bubbles are generated on the individual heating body mounting faces and sequentially flow downstream (to the radiator 3100), therefore, the bubbles are the more in the refrigerant tank 3110 as they approach the closer to the radiator 3100. This makes the more liable for the burnout to occur on the heating body mounting face the closer to the radiator 3100. In order to prevent this burnout on the heating body mounting face closer to the radiator 3100, on the other hand, it is necessary to enlarge the thickness size of the refrigerant tank 3110 thereby to increase its capacity. This increases the quantity of refrigerant to be reserved in the refrigerant tank 3110, thus causing a problem to invite a high cost.
Further still another conventional cooling apparatus is disclosed in Japanese Patent Application Laid-Open No. 8-236669. This cooling apparatus forms a vaporized refrigerant outlet 4120 and a condensed liquid inlet 4130 by arranging a refrigerant control plate 4110 obliquely in the upper portion of a refrigerant tank 4100, as shown in FIG. 81. Thus, the vaporized refrigerant, as boiled in the refrigerant tank 4100, can flow out along the refrigerant flow control plate 4110 from the outlet 4120, and the condensed refrigerant, as liquefied in a radiator arranged in the upper portion of the refrigerant tank 4100, can flow from the inlet 4130 into the refrigerant tank 4100. As a result, the interference between the vaporized refrigerant to flow out from the refrigerant tank 4100 and the condensed liquid to flow into the refrigerant tank 4100 can be reduced to improve the refrigerant circulation in the refrigerant tank 4100.
In the further still another cooling apparatus in FIG. 81 using the refrigerant control plate 4110, however, the vaporized refrigerant outlet 4120 is opened obliquely upward so that the condensed liquid dripping from a radiator cannot wholly flow from the inlet 4130 into the refrigerant tank 4100. That is, any portion of the condensed liquid dripping from the radiator will flow in any event from the outlet 4120 into the refrigerant tank 4100 to establish the interference between the vaporized refrigerant and the condensed liquid. As the radiation rises, therefore, the interference between the vaporized refrigerant and the condensed liquid becomes serious so that a reduction in the radiation performance may occur.